cvs commit: src/sys/ufs/ufs ufs_lookup.c

[Scott Long]

Eric Anderson wrote:
> Ruslan Ermilov wrote:
> 
>> On Wed, Mar 08, 2006 at 03:16:25AM -0500, Kris Kennaway wrote:
>>  
>>
>>> On Wed, Mar 08, 2006 at 09:06:32AM +0200, Ruslan Ermilov wrote:
>>>    
>>>
>>>> On Wed, Mar 08, 2006 at 02:14:39AM +0000, Tor Egge wrote:
>>>>      
>>>>
>>>>> tegge       2006-03-08 02:14:39 UTC
>>>>>
>>>>>   FreeBSD src repository
>>>>>
>>>>>   Modified files:
>>>>>     sys/ufs/ufs          ufs_lookup.c   Log:
>>>>>   Don't set IN_CHANGE and IN_UPDATE on inodes for potentially 
>>>>> suspended
>>>>>   file systems.  This could cause deadlocks when creating snapshots.
>>>>>     Reviewed by:    jeff
>>>>>     Revision  Changes    Path
>>>>>   1.80      +0 -1      src/sys/ufs/ufs/ufs_lookup.c
>>>>>
>>>>>         
>>>>
>>>> Like for example "ls -l /filesystem/.snap" when "fsck -B" is in place?
>>>>       
>>>
>>> Is that a deadlock, or just the process being suspended until fsck
>>> finishes?
>>>     
> 
> 
> I think the only options we have to fix this is to either make the .snap 
> directory 'hidden' (which is not a feature yet), or to possibly cache 
> the inode information on parent directories containing snapshots, so 
> when a fs is suspended or a snapshot is in progress, a stat of the 
> parent directory of the snapshots' doesn't block until the snapshot 
> finishes.
> There has been brief discussion on freebsd-fs@ about adding a 'hidden' 
> flag (usable with chflags) to files and directories, and tools like ls, 
> etc, that would normally stat each file/dir in a directory would ignore, 
> unless a special option was used.  That would not stop other tools doing 
> stat calls from seeing it though, but I think most of the blocking 
> happens when a user does an ls -al in the directory.
> 
> 
> Eric
> 
> 
> 
> 

The only way to effectively avoid the problem would be to teach UFS to
completely ignore the '.snap' directory entry when doing a readdir and
lookup.  That is not the same as what is being discussed with having a
special hiiden hint flag.

Scott